Ultra fine particles, e.g. metal oxides, organic compounds, inorganic compounds, and composite particles, can be used as new materials with high performance in microelectronics, information industry, aviation industry, chemical engineering, mechanical engineering, auto industry, bioengineering, etc. At present, the production of ultra fine particles can be classified into physical methods and chemical methods. Among the chemical methods, the precipitation method is the most common one, where a chemical precipitation reaction takes place in a stirring tank reactor or a mixing kettle reactor and in an ordinary gravitational field. The precipitation method has the following disadvantages: (1) non-uniform distribution of the particle sizes and difficult in controlling the particle size; (2) poor repeatability between batches of product; (3) slow mass transfer, long reaction time, large energy consumption, and low production efficiency. These disadvantages mainly are caused by non-uniform micro-mixing in the reactor, and poor micro-mass-transfer, etc.
U.S. Pat. No. 4,283,255 by Ramshaw, et at. (1981) disclose a technique for performing a mass transfer through a rotation pack bed. This technique is mainly used for the gas-liquid contact and the reaction thereof, wherein a pack bed rotating at a high speed is used to increase the liquid-gas mass-transfer efficiency. Similar rotation pack beds can also be found in U.S. Pat. Nos. 4,382,045; 4,382,900; and 4,400,275.
In 1996,Jiann-Feng Chen et al. disclosed (CN1116185A) an ultra-gravity method for preparing an ultra fine powder of calcium carbonate, wherein a carbonization reaction performing in a reaction vessel is improved by using an ultra-gravity reaction device. Said method reduces the carbonization time and enables the particles becoming ultra-fine, where the particle size can be controlled at 10˜100 nm with a uniform particle distribution.
In 2000, Jiann-Feng Chen et al. published (CN1258639A) a method for preparing an ultra fine powder of aluminum hydroxide by an ultra-gravity method, which comprises decomposing the carbon-containing compounds, and water-heating treatment. After the water-heating treatment, the particle size can be controlled at 1˜5 nm, and a needle-like crystal with an aspect ratio of 5˜100 can be obtained.
In 2001, Jiann-Feng Chen et al. published (CN1288856A) an ultra-gravity method for preparing an ultra fine powder of silicon dioxide, wherein an ultra-gravity reaction device is used to effectively reducing the carbonization time of water glass, thereby obtaining an ultra fine powder of silicon dioxide having a particle size of 15˜30 nm.
In 2001, Han et al. published a water-heating method for preparing an ultra fine powder of ferric oxide (U.S. Pat. No. 6,203,774), which comprises dissolving α-FeOOH in ethanol, and using a water-heating method together with a habit modifier to control the crystal pattern of the ferrous oxide obtained.
The use of an ultra-gravity device (rotation pack bed) has the following disadvantages: (1) non-uniform mass transfer efficiency, with the efficiency gradually decreasing towards the outer periphery of the rotation bed; (2) easy to form a situation where the density of the packing near the outer periphery is higher than that of the portion near the rotation axis due to the centrifugal force; (3) the rotation pack bed having a complicated structure such that the bed is liable in losing its dynamic balance and causing a frequent shut-down for maintenance.
A primary objective of the present invention is to provide a reactor for producing ultra fine particles, which is free of the abovementioned disadvantages.
Another objective of the present invention is to provide a reactor for producing ultra fine particles, which has an enhanced mixing efficiency.
A further objective of the present invention is to provide a method for preparing ultra fine particles.
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10 . . . reaction chamber 1 . . . liquid inlet pipe 2 . . . perforation 3 . . . gas inlet 4 . . . external frame 5 . . . stainless steel screen 6 . . . rotation shaft 7 . . . reaction product outlet 8 . . . gas discharge pipe 20, 20′, 20″, 20a . . . porous rotors 30 . . . rotation table